Rep. Jesse Jackson Jr. reportedly will resign from Congress, according to the Chicago Tribune.

The newspaper quotes Jackson's brother, Jonathan, as a source. The Illinois Democrat, first elected in 1995, is expected to send a letter of resignation "momentarily" to House Speaker John Boehner.

Jackson, the son of the civil rights leader, has been on medical leave since mid-June and twice sought treatment at the Mayo Clinic for bipolar disorder. He was easily re-elected to a ninth full term, even though his constituents haven't seen or heard from him in months.

Once considered a rising Democratic star, Jackson is being investigated on allegations that he misused campaign funds to pay for redecorating his house and an expensive watch for a friend.

Jackson hired former federal prosecutor Dan Webb to work out a plea deal on the campaign finance allegations. CBS News said the deal would likely include jail time.

The congressman also has been the subject of a long-running House Ethics Committee investigation stemming from allegations that he raised money for then-Illinois governor Rod Blagojevich in exchange for appointment to the U.S. Senate. Jackson has denied wrongdoing.